But also for a simple vessel I recommend to use this method. In those situations the standard formulation of hydrostatic stiffness becomes extremely complicated. Especially if the vessel is composed of multiple elements such as cranes, cargo is placed on it or lifted from it or multiple vessels elements are interconnected. This may sound difficult but it actually makes many things a whole lot easier. It also introduces an alternative way of modeling the hydrostatics by removing the gravity effects from the stiffness matrix. This guide presents a step-by-step guide for setting up a vessel with first order diffraction data from orcawave. Setting up the vessels for such a model using orcaflex is easy but not trivial, but in the end it is just book-keeping. Is that a result of conventional differences between the two tools or just I get it the wrong way? The hydrostatic stiffness matrix you give in the document Definition of the Semisubmersible Floating System for Phase II of OC4 also does have the negative value, but isn't all the values in a stiffness matrix supposed to be positive?ģ.Many offshore operations can be modeled using first order time domain analysis.
When I try to do a free decay analysis in orca alone, it seems like that I have to change the negative values in the hysrostatic stiffness matrix to positive so I can do the analysis.
So I am confused because if it is to balance the gravity, isn't it supposed to get balance when i input the value in the vessel mass and inertia data?Ģ. But the vessel won't get balanced and it only does when I uncheck the applied loads. But when I try to do a free decay analysis with orcaflex alone, I set the platform primary motion to "calculated(6 DOF)" and input the mass and inertia data in the vessel type data.
In the orca model, there is a applied loads acting on the vessel whose value is 140E6, what is that for?Īs far as I know, the applied load is equal to the gross gravity of the platform+tower+nacelle, so I assume that is for the gravitional equilibrium. But there are some settings in the Orca model that confused me and hope you may help me out. I've downloaded the Sample models for FAST and OrcaFlexInterface ( ) and tried to modify the OC4_DeepCwind model so I can use it in the second order hydrodynamis analysis.
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